Capacity sensitive relays



Dec. 9, 1958 v, CQLES ET AL 2,863,472

CAPACITY SENSITIVE RELAYS Filed Sept. 8, 1954 INVENTORS Rad viz I Galesand y Michael Bayey wA/ /M THE IR 41 0" OBZVE'Y "United States 'Patent2,863,472 CAPACITY SENSITIVE RELAYS Ralph V. Coles, Radnor, and MichaelBagley, Philadelphia, Pa., assignors to Robertshaw-Fniton ControlsCompany, Greensburg, Pa, a corporation of Delaware Application September8, 1954, Serial No. 454,746 Claims. (*Cl. 137-4592) This inventionrelates to capacity sensitive relays and more particularly to capacitytype high level fail-safe control switches.

It is an object of this invention to control a relay for operating apump in response to slight variations in a controlling capacity.

Another object of this invention is to prevent the possibility of avessel running over in the event of line voltage failure or tubefilament burn out.

Still another object of this invention is to indicate a high level inthe event of line voltage failure or tube filament burn out.

With these and other objects in view, the invention may take the form ofan oscillator circuit including an oscillatory tank circuit coupled toan electron discharge tube with a source of alternating voltage for theanode of the electron discharge tube. A work circuit including a relayis connected in the anode circuit of the discharge tube and serves tooperate a pump switch and an indicator light depending upon the normaloperation of the device. A capacity sensitive probe is connected to theoscillatory tank circuit and is utilized to pick up the straycapacitance which varies according to the level of the fluid in a vesselthereby varying the feedback generated in the tank circuit. Relayoperated switches are aifected by the current developed in the anodecircuit to cause a high level indication. With this arrangement,operation of the pump is prevented in the event of circuit failurecaused by power failure or tube filament burn out, such failure beingindicated as high level.

Other objects and advantages will become apparent from the followingspecification taken in connection with the accompanying drawing in whichthe single figure is a diagrammatic showing of the essential elements ofa capacity sensitive relay embodying this invention.

Referring more particularly to the drawing, the system embodying thisinvention is shown as comprising an oscillator circuit controlling theoperation of a relay 12, a probe 14 for picking up stray capacitance forthe oscillator circuit 10 and a pump 16 operable in response to to theenergization of the relay 12.

The oscillator circuit 10 comprises an electron discharge tube 18 havingan anode 20, cathode 22, grid 24 and cathode heater 26. Coupled to theelectron discharge tube 18 is an oscillatory tank circuit consisting ofa coil 28 connected in parallel with a capacitor 36, one end of the coil28 being grounded at 32. Completing the tank circuit are capacitors 34,36 connecting the ends of the coil 28 to the parallel circuit ofcapacitor 31?. The cathode 22 of the tube 13 is connected to a centertap in the coil 28. The anode of the tube 18 is coupled to one end ofthe tank circuit through a blocking capacitor 38. interposed between thegrid 24 and capacitors 3t 34 is thet grid leak resistor 46.

Power is supplied to the oscillator circuit 10 by a transformer 42, theprimary winding of which is connected across a source of alternatingcurrent supply and indicated by lines L1, L2. A secondary winding 44 ofthe transformer 42 has a tap 46 grounded at 48. One terminal of thesecondary winding 44 is connected to the cathode heater 26 and thencegrounded at 50 while the other terminal 52 is coupled to the oscillatorcircuit 10 by a lead 54 to the anode 20 and by a lead 56 to the centertap of the coil 28. A suitable capacitor 58 and a ice 2 small R. F.choke 60 are in series in this anode circuit. The terminal 52 of thesecondary winding 44 is also connected to the anode 26 of the electrondischarge tube 18 through the exciter coil 62 of the relay l2 thencethrough the lead 64 to the anode circuit and connected thereat betweenthe capacitor 58 and the choke 60.

As is shown in the drawing, the relay 12 is equipped with a movablecontact 66 which engages a fixed contact 68 to operate the necessarypump circuit to be described hereinafter, when a change occurs in acondition of the oscillator circuit 10. Mechanically coupled to themov-- able contact 66 is a second movable contact 70 which engageseither one of two fixed contacts 72, 74 of an indicator system includinga high level red lamp 76 and a low level green lamp 78, respectively. Asuitable lead connects fixed contact 72 to the lamp 76 and anothersuitable lead connects fixed contact 74 to the lamp 78. Suitable leadscomplete the indicator circuit to the center tap of the secondarywinding 44.

The control apparatus of this invention may be of the usual industrialtype comprising a closed container 80 wherein 82, 84 represent variouslevels of fluid in the container and the supply pipe 86 supplying thecontainer 86 from any suitable source (not shown). The pump 16 isinterposed in the pipe 86 and serves to pump fluid in the container atpredetermined conditions to be described hereinafter. The pump 16 may beof any wellknown type having a conductor 88 connected to supply line L1and another conductor 96 connected to the movable contact 66 of therelay 12. The conductor 92 completes the relay and pump circuit to thesource of electrical supply.

That portion of the mechanism of the invention which constitutes thecontrol mechanism therefor, and may be located at a point near the topportion of the closed container 8! is as follows: Mounted on the closedcontainer 80 is the probe 14 having its electrode 94 secured thereto byany suitable insulated mounting means 96. The electrode may consist of abare extremity exposed to the atmosphere above the fluid level and maybe of any desired construction. A conductor 93 connects the electrode 94to the oscillator circuit 19 and is shielded by a shield which isgrounded at 102. The capacitance between the electrode 94 and the groundis effectively in parallel with the capacitor 36 and is the varyingelement of the inductance-capacitance bridge circuit consisting of thecapacitors 34, 36, 3t) and the two portions of the coil 28.

Operation Assuming that the fluid level in the closed container 8t? isat level 84 and the green lamp 76 is energized for indicating the closedpump circuit and the low level of the fluid, the impedance ratio ofcapacitors 34, 36 is greater than the impedance ratio of the two halvesof coil 28 and the positive feedback to the tank circuit is insufficientto sustain oscillation. Since discharge tube 18 is not oscillating, itis conducting current at its maximum rate thereby energizing relay 12 sothat the movable contact 66 engages the fixed contact 68. This allows acontinuing source of electric current to energize the pump 16 and fluidcontinues to flow into the container 86. As the fluid level rises towardthe electrode 94, the capacitance between electrode 94 and groundincreases because the surrounding air having a dielectric constant of(1) is replaced by a material of some higher dielectric constant. Theincrease of capacitance between electrode 94 and ground beingeifectively added to capacitor 36 decreases the impedance ratio ofcapacitors 34, 36. When the level of the fluid reaches level 82 and isin contact or near contact with the electrode 94, the impedance ratiobetween the two halves of the coil 28 becomes greater than the impedanceratio of the capacitors 34 36 whereby a positive feedback is generatedand the grid 24 will be supplied with alternating potential of theproper phase to initiate and sustain oscillation. The oscillationdevelops a grid leak bias on the resistor 4d which greatly reduces theanode current of the discharge tube 1'8 causing the deenergization ofthe relay 12 where it follows that the movable contact 66 will becomedisengaged from the fixed contact 68 and the movable contact 7@thereupon will be rotated from the fixed contact 72 to the fixed contact'74. From this it is obvious that the circuit to the pump 16 is open andthe red indicator lamp 78 energized while the green indicator lamp '76is deenergized. v

The control apparatus of the invention operates as a capacity type highlevel fail-safe control switch since in the event of power failure orfilament tube burn out, the relay 12 will be deenergized or remain inits deenergized position. The level of the fluid in the container 8hwill appear to be at the level 82 regardless of its actual level in thecontainer, such appearance being indicated by the red lamp '78. Ineither event, that is, if the level of the fluid is at 82, or there is afailure in the circuit, the operator of the control apparatus will bewarned that 1 the tank is either filled or that the system isinoperative without experiencing the danger of an overflowing container.

It will be apparent to those skilled in the art that many modificationsof the disclosed embodiment of this invention may be made withoutdeparting from the scope thereof, which is to be measured by theappended claims.

We claim:

1. In a device for controlling the level of fiowable material in acontainer, the combination comprising an oscillator circuit including ananode, a cathode, a grid and a tank circuit, a source of voltageconnected to said anode, a probe capacitor operatively connected to saidtank circuit and sensitive to variations inthe level of said flowablematerial to decrease the conductivity of said tube with increase in thelevel of said fiowable material in said container, a relay circuitconnected to said anode and including a control switch operable to aclosed position for supplying fiowable material to said container inresponse to an increase in conductivity of said tube, an indicatingcircuit connected to said source including electric indicating means anda switch connected to control energization of said indicating means, andmeans including said relay circuit for actuating the last said switch toenergize said indicating means.

2. In a device for controlling the level of flowable material in acontainer, the combination comprising an oscillator circuit including ananode, a cathode, a grid and a tank circuit, a source of voltageconnected to said anode, a probe capacitor operatively connected to saidtank circuit and sensitive to variations in the level of said flowablematerial to decrease the conductivity of said tube with increase in thelevel of said fiowable material in said container, a relay circuitconnected to said anode and including switch means operable from oneposition to another in response to a decrease in the conductivity ofsaid tube, means including said switch means for supplying flowablematerial to said container in re sponse to an increase in conductivityof said tube, and means including said switch means for indicating thelevel of flowable material in said container.

3. In a device for controlling the level of a flowable material in acontainer and having a source of voltage, the combination comprising anoscillator circuit including an electron discharge tube having an anode,a cathode, a grid and a tank circuit, means including an inductivemember for connecting said anode to the source, capacitive meansconnecting said anode to said tank circuit, a probe capacitor associatedwith said tank circuit and sensitive to variations in the level of thematerial to decrease the conductivity of said tube in response to anincrease in the level of the material and to increase the conductivityin response to a decrease in the level of the material, a relay circuitconnected to said anode including a switch operableto a closed positionfor supplying flowable material to the container in response to anincrease in conductivity of said tube, and indicating circuit connectedto the source and including first and second indicating lamps, and asecond switch for controlling said indicating circuit associated withsaid relay circuit and having a first position for energizing said firstlamp and a second position for energizing said second lamp, said secondswitch being operative from said first position to said second positionin response to an increase in the conductivity of said tube.

4. In a device for controlling the level of a fiowable material in acontainer and having a source of voltage, the combination comprising anoscillator circuit including an electron discharge device having ananode, a cathode and a grid, an oscillatory tank circuit operativelyconnected to said grid and including an inductive member having one endthereof connected to one side of the source, means including inductivemeans for connecting the other side of the source to said anode,capacitive means for connecting said anode to the other end of saidinductive member, means for connecting the electrical center of saidtank circuit to said cathode, a probe capacitor operatively associatedwith said tank circuit and sensitive to variations in the level of saidmaterial to decrease the conductivity of said tube in response to anincrease in the level of the material and to increase the conductivityin response to a decrease in the level of the material, a relay circuitconnected to said anode including a switch operable to a closed positionfor supplying flowable material to the container in response to anincrease in conductivity of said tube, an indicating circuit connectedto the source including first and second indicating lamps, and a secondswitch for controlling said indicating circuit associated with saidrelay circuit and having a first position for energizing said first lampand a second position for energizing said second lamp, said secondswitch being operative from said first position to said second positionin response to an increase in the conductivity of said tube.

5. In a device for controlling the level of a fiowablc material in acontainer and having a source of voltage, the combination comprising anoscillator circuit including an electron discharge device having ananode, a cathode and a grid, an oscillatory tank circuit operativelyconnected to said grid and including an inductive mam her having one endthereof connected to one side of the source, a choke means connectingsaid anode to the other side of the source, a by-pass capacitorconnecting said anode to the other end of said inductive member, meansfor connecting the electrical center of said tank circuit to saidcathode, a probe capacitor operatively associated with said tank circuitand sensitive to the variations in the level of the material to decreasethe conductivity of said tube in response to an increase in the level ofthe material and to increase the conductivity in response to a decreasein the level of the material, a relay circuit connected to said anodeincluding a switch operable to a closed position when said tube isconducting, said switch being operative to control the supply offiowable material to said container, and means to indicate theenergization of said relay when the level of said flowable materialreaches a point adjacent said probe.

References (Cited in the file of this patent UNITED STATES PATENTS2,635,225 Hadady Apr. 14, 1953 2,655,933 Odell Oct. 20, 1953 2,763,283Grimth et al. Sept. 18, 1956 FOREIGN PATENTS 663,643 Great Britain Dec.27, 1951

